Frequency-compensated flowmeter system



- March 21, 1961 s. E. RosE 2,975,634

FREQUENCY-COMPENSATED FLOWMETER SYSTEM Filed Aug. 17, 1955 STANLEY E. ROSE AGENT Urli@ Sete Pete This invention relates to apparatusfor the gravimetri measurement Vof liquid quantity. l The Vmeasurementv of sizeable quantities of flowing liquid with accuracy is a diliicult problem.Y `In certain aeronautical applications this dicult task is rendered 'even more complex bythe environment. In one application, that. of metering fuel transferred in mid-air from an airborne tankerv aircraft to a second aircraft the ,fuelingrrate may be as high asf800,000 pounds-per hour.

` This vrate is far above the capability of conventional 'metering devices. v |In still a dilferent application there sa requirement 'for improved fuel quantity measuring apparatus suitable `for use with-odd shaped storage cells. For example the thinness and shapeof advanced design supersonic lighter aircraft wings may require anY unreasonable number'- f fuel tank probes if capacitance type gages are used. A4 study of a typical supersonic Ytighter revealed Vthat overseventy wing "probes would be required. Beside .tli-is'large quantity ofprobes, other complications appeared such as the inaccessibility of the probes and probe 4connecting Wires within the wing. By way of contrast, the device of this invention may be readily installed in the existing fuelv lines of an aircraft at the point where they emerge from the wing into thefuselage thus avoiding installing in the wing of any additional equipment exclusively for fuel quantity gaging.

Being located in the fuselage, the instruments are readily vavailable for servicing.

f When the unit is employed as a fuel quantityfgage, it 'acts as a'bidirectional ilowmeter. The device counts the pounds of fuel pumped into say, the wing tank. As fuel' isfused or transferred to fuselage tanks, `the instrument counts the pounds of fuel removed from the tank, sub- Y vtractsl it from the total and shows, on-a suitableindicator the quantity' of-fuel Iremaining in the tank. ,l For aircraft use it lis Vimportant'that equipment be rugged, compact and light in weight.

" l'Briey stated, the apparatus of this'inven'tion "includes two wheels through whichthe flow of fuel 'isY channeled. One wheel; the impeller wheel is drivenv by a synchronous 'motor and the other wheelfa VsensingA wheel isgearedtd-a torquemotor. y 'i' Inl `the case of a bidirectional unit,` such as a *flowmeter used as a fuel quantity gage, three wheels are used, two asi'rnpellers and one for sensing.

' 1 lThe -impeller wheel imparts angular momentum to fuel being directly proportional tov flow rate, is used to actuate an indicating means. The signal may be integrated to show total quantity.-

It is to be noted that the apparatus of this invention measures actual mass whereas owmeters in general are volumetric devices. The pilot of an airplane is concerned with lthe energy value of his fuel supply as represented by its weight rather than its volume.

Accordingly, it is an object of this invention to provide `an accuratelhigh rate owmeter.

It isanothery object of this invention to provide a lightlweight owmeter. I f

:ItV is: arpairticular object of 'this Iinvention to provide aflowmeter capablel of ccurateindication and which does not require an accurately regulated power source'. '15A Afurtherobject of this invention is to provide an improved liquid quantity measuring system.

Still a different objectV is to provide a true mass measuring flowmeter. Another object of this invention'is to provide a owmeter driven by a synchronous motor.

An` object of this invention is to *provide a owmeter which may be equipped with remotely located indicating means. i v

Still other objects, advantages and desirable features of the' invention will become apparent from the following description and by reference to the following drawings, in which: i

Figure 1` shows the vector relationship of the velocity of the liquid passing through the impeller wheel and sensing wheel of the owmeter. I Figure'Z shows partly pictorially and partly schematically a ilowmeter'with a portion of the housing cut-away so =as to exposeimpeller and sensing wheels and `other elementsof the device. v

Like reference characters are to refer to like elements. Y,

The principle of operation of the true mass owmeter of this invention is the utilization of signal'torques `resulting from the conservation of the moment of momentum. This principle is embodied by imparting an angular momentum to the mass influx of lluid 8 through the conduit formed by housing `10 by means of an impeller wheel 145driven by a synchronous motor 12 through gear 13. The blades 16 are mounted in a hub atzero degrees angle of incidence with respect tothe direction of flow. This moment of momentum is then extracted from the huid S by means `of a second wheel 18 which serves as a sensing wheel. Wheels 14 and v18 are supported by means of low friction bearings (not shown) from shaft`19. In turn shafty 19 is supported by ns 20.

The torque, exerted on wheel 18 isfound in practice used i in the drawings to be proportional to the mass llow rate in accordance passingV through it. This impinges on the sensing wheel Ylitfisigeared. v Y ".If the motors torque doesnt equal the torque dev eloped in the sensing wheel, a net torqueresults which rotates a gear train.

tending to rotate it and buck the torque motor to which I:to 'the torque motor to produce a torque which exactly A pick-off potentiometer, driven .-15 hq gear train, provides a voltagevvhich is related ,to. 6W rate. This voltage is ampliedand fed back .talante-...the seeing, uhsefefque sans yeltage s.

' MBy the impulse-momentum` principle with the following derivation.

p Fdf=,d(MV) 1 I(1') The force required for 'a change in momentum from V1 to V2 velocity vectors shown in Figure 2 is Where vp is the mass density q is the volumetric ilow rate thru one set of vanes and (V2- V1) is the vector subtraction of the velocity vectors shown. A

vBut VTI/1:7, Y v(s) *where ris the geometric mean radius andrew isit'hey angu- ...zlr ,vslssity sf the impeller-wheel. f

The torque on the sensing wheel 18 is then:

T=F=pQr2w (4) Where Q is the volumetric tlow rate through all chambers in the sensing wheel 18.

But pQ is the mass flow rate M. Therefore the torque on sensingl wheel 18 is directly proportional. to the mass flow rate and the angular velocity of the impeller wheel 1-4.

Generally speaking it is the primary object of the invention to display this mass flow rate on a suitable indicator. In order to. accomplish this conveniently the torque signal must be transduced. into an electrical signal which is then transmitted to a remotely located indicator 21. Indicator 21 may be ofthe moving coil type. Many suitable voltage indicating devices are commercially available and therefore need not be described herein in detail.

To derive a voltage proportional to the torque on the sensing wheel 18, a torque balance between the torque from a torque motor 22 and the sensing wheel torque is made 4by adjusting the voltage E0 applied to torque motor 22 until balance is obtained. This balance is achieved by using the unbalanced torque to rotate the sensing wheel 18 and an angular position sensing means 24 by means of gears 23 and 25. The position sensing means 24 is adapted to produce an output signal proportional to angular position. A rotational type potentiometer may be employed as the position sensing -means 24. The voltage from sensing means 24 is amplified by amplifier 26 and applied in turn to motor 22. The torque motor 22 will rotate to a position wherein the amplified output of sensing means 24 is of sufficient magnitude and proper polarity to cause the motor torque to just balance the fluid flow torque. The voltage En is therefore proportional to mass flow rate and if indi- 'cator 21 is chosen to have a response proportional to rate.

In aircraft applications it is convenient to operate syn- 'chronous motor directly from the aircraft power supply which is nominally 115 volts 400- vapproximately plus or minus Since the speed of a synchronous motor is a function of line frequency the angular momentum imparted to the fluid will vary as the frequency. The torque imparted to the sensing wheel by the fluid is directly proportional to the mass ilow rate and the angular velocity of the impeller wheel 14. Therefore, the torque motor 22 will drive the sensing wheel to a position at which the angular position sensing means 24 pro- 'duces an output voltage proportional to the torque on the sensing wheel and the torque motor .22 produces a torque substantially equal and opposite the imparted torque. Since the torque varies as the frequency varies, the output voltage of the angular position sensing voltage output means 24 will vary in response to variation of the supply frequency. Since the indicator is responsive to the output voltage ofv voltage output means 24, the indicator reading will include an error because of the variation in the frequency of the supply voltage. As a compensation means there is employed a frequency sensitive voltage varying means 30, shown as an R-C phase shift network composed of resistor 32 and capacitor 34. The frequency sensitive means 30 is interposed between the voltage output means 24 and the indicator 21 so as to vary the output voltage in accordancewith the frequency of the signal whereby the 4indicator provides an indication independent of the frequency of the power supply voltage.

The conventional engineering solution to the problem introduced by the varying frequency would be the use of a stabilized power source, a heavy, bulky and ex- 'pensive device, but one which is commonly employed.

It is indeed `a uniquesolution to apply' a simple', light- E0 the indication will be proportional to the mass ow weight and inexpensive resistance-capacitance network that can accomplish the same result.

As discussed above the device is capable of measuring flow in but one direction. In a typical application for the device it is desired to register the amount of fuel consumed so that the indicator 21 serves as a quantity gage. For bi-directional use it is necessary to provide a second impeller wheel 38l which is coupled to impeller wheel 14 by means of gears 40, 41, 42 and 43 and shafts 44 and 45. Gears V4,1 and 42serve to reverse the direction of rotation of impeller wheel' 38. 'Ihis permits the use of but one motor to drive both impeller wheels. Two separate motors'may also be used. Where quantity indication is desired indicator 21 should be of the diierential integrating type.

The number of vanes employed in impeller and sensing wheels should differ by some number other than a multiple so as to avoid locking in between wheels as is common in fluid drive mechanisms.

It is to be understood that the inside of housing 10 closely surrounds impeller wheels 14 and 38 and sensing wheel 16v and that the auxiliary equipment such as motors 12 and 22 and sensing means 24 fit into cavity 50 and gears 40, 41, 42 and 43 fit into cavity 52. Thus virtually the entire liquid flow is directed through vanes 16 of the respective wheels.

It will be understood that the invention can be used for different purposes or carried out in different ways by other forms of apparatus than described herein, and it is not intended to limit the scope of the invention to the specific arrangements ldescribed or otherwise than by the terms of the appended claims.

What is claimed is:

l.v In an apparatus for measuring the mass flow rate of a flowing fluid adapted to be energized by a source of A.C. power including a rotatable vane type first impeller wheel; a synchronous motor, adapted to be energized from the source of A.C. power, coupled to said impeller wheel; la vane type sensing wheel; means for supporting said impeller wheel and said sensing wheel coaxially in juxtaposition; conduit means for directing said flowing fluid, in turn, through said impeller wheel and said sensing wheel so that rotation of the impeller wheel imparts to said fluid angular momentum whereby said sensing wheel has exerted upon it, by the resulting angularly accelerated fluid, a torque related to the mass flow rate of said flowing fluid and the angular velocity of said impeller Wheel, the improvement comprising: angular position measuring voltage output means coupled to said sensing wheel so as to provide an output voltage related to the angular position of said sensing Wheel, a torque motor coupled to said sensing wheel; means electrically connecting said torque motor with said angular position detecting voltage output means whereby said torque motor is under the control of said angular position detecting voltage output means so as to act `on said sensing wheel with a torque substantially equal and opposite said torque exerted on said sensing wheel by said fluid; and indicating means, for indicating said flow rate, electrically connected to said angular position detecting voltage output means land under the control thereof.

2. The apparatus of claim 1 including a frequency sensitive voltage varying means interposed betweensaid angular position detecting voltage output means and said indicating means, said frequency sensitive voltage varying means being adapted to vary the said output voltage to compensate for variation in the frequency of the A.C. power source.

3. The apparatus of claim 2 wherein said frequency sensitive voltage varying means comprises a resistor in cascade with said angular position detecting voltage output means and said indicating means and a capacitor in shunt connection with saidresistor.

4'. A bidirectional integratingtype'mass flowmeterffr measuring the quantity of a flowing uid and adapted to be energized by a source of A.C. power including a rotatable vane type first impeller wheel; a synchronous motor, adapted to be energized from the source of A.C. power, coupled to said impeller wheel; a vane type sensing wheel; means for supporting said impeller wheel and said sensing Wheel coaxially in juxtaposition; conduit means for directing said flowing fiuid, in turn, through said impeller wheel and said sensing wheel so that rotation of theimpeller wheel imparts to said fluid angular momentum whereby said sensing wheel has exerted upon it, by the resulting angularly accelerated fluid, a torque related to the mass flow rate of said owing tiuid and the angular velocity of said impeller wheel; angular position measuring voltage output means coupled to said sensing wheel so as to provide an output voltage related to the angular position of said sensing wheel; a torque motor coupled to said sensing wheel; means electrically connecting said torque motor with said angular position detecting voltage output means whereby said torque `motor is under the control of said angular position detecting voltage output means so as to act on said sensing wheel with a torque substantially equal and opposite said torque exerted on said sensing wheel by said fluid; a second impeller wheel mounted coaxially with said first impeller wheel and adjacent to said sensing Wheel with said sensing Wheel interposed between said frst and said second impeller wheels; a gear train couplingsaid first and said second impeller wheels so as to contrarotate said second impeller wheel with respect to Isaid iirst impeller wheel; integrating indicating means connected to said angular position detecting voltage output means, said indicating means being responsive to said output voltage so as to provide an indicationof the dilerence in quantity. of uid passing lthrough said sensing wheel from said first impeller wheel and the quan tity of uid passing through said sensing wheel from said second impeller wheel.

5. In a bidirectional apparatus .for measuring the mass flow rate of a iiowing uid and adapted to be energized by a source of A.C. power including la rotatable vane type first impeller wheel; a synchronous motor, adapted to be energized from the source of A.C. power, coupled to said impeller wheel; a vane type sensing wheel; means for supporting said impeller wheel and said sensing wheel coaxially in juxtaposition; conduit means for directing said owing uid, in turn, through said impeller wheel and said sensing wheel so that rotation of the impeller Wheel imparts to said Vfluid angular momentim whereby said sensing wheel has exerted upon it, by the resulting angularly accelerated fluid, a torque related to the mass ow rate of said ilowing Huid and the angular velocity of said impeller wheel; angular position measuring voltage output means coupled to said sensing Wheel so as to provide an output voltage related to the angular position of said sensing wheel, a torque motor coupled to said sensing wheel; means electrically connecting said torque motor with said angular position detecting voltage output means whereby said torque motor is under the control of sai-d angular position detecting voltage output means so as to act on said sensing wheel with a torque substantially equal and opposite said torque exerted on said sensing wheel by said fluid; a second impeller wheel mounted coaXially with said first impeller Wheel and adjacent to said sensing wheel with said sensing wheel interposed betweensaid first and said second impeller wheels; a gear train rcoupling said first and said second impeller wheels so as to contrarotate said second impeller wheel with respect to said first impeller wheel; indicating means connected to said angular position detecting voltage output means, said indicating means being responsive to said output voltage so as to provide an indication of the mass flow rate of iuid passing through said sensing wheel.

6. The apparatus of claim 5 including a frequency sensitive voltage varying means interposed between said angular position detecting voltage output means and said indicating means, said frequency sensitive voltage varying means being adapted to vary the said output voltage to compensate for variation in the frequency of the A.C. power source.

References Cited in the iile of this patent UNITED STATES PATENTS 789,110 Warren May 2, 1905 1,152,952 Kepka Sept. 7, 1915 2,183,078 Kemler Dec. 12, 1939 2,231,702 Burgwin et al Feb. 11, 1941 2,361,173 Browne Oct. 24, 1944 2,601,780 Baecher July 1, 1952 2,605,638 Pearson Aug. 5, 1952 2,714,310 Jennings Aug. 2, 1955 2,769,337 Rich Nov. 6, 1956 FOREIGN PATENTS 717,897 Great Britain Nov. 3, 1954 

